The invention relates to the electrical scanning of luminous images in successive lines forming frames, using a charge transfer device incorporating a line memory.
Various solid state devices scan an image and supply a television camera with a video electrical signal. They differ in the way in which the photosensitive zone is formed and in the system for reading and removing the charges produced by the image.
Charge transfer devices perform these, as described, for example, by SEQUIN and TOMPSETT, in "Charge Transfer Devices", pp. 152 to 169. In "frame transfer" or "interline structure" organisations the light radiation is received on charge transfer registers. The charge transfer then takes place over large areas, which is a disadvantage, since it is difficult to obtain high efficiency levels for such large areas. CID's (charge injection devices), do not have these disadvantages, but generally require reinjection of the charges into the semiconductor substrate, resulting in noise and difficulties in connecting with the capacitance values during and after reading.
There is also the question of compatibility between the time necessary for light integration and for charge transfer when the latter solution is adopted e.g. with the sweep time of the television screen. A 625 line standard, these times are generally about 52 .mu.s for the display time of a line and 12 .mu.s for the line return time.
In order to meet these different requirements, the Applicant Company has proposed a so-called "line transfer" structure, described in U.S. Pat. No. 4,430,672. This structure has a matrix of N lines.times.M photosensitive zones or points onto which an image to be scanned is projected and converted into electric charges called signal charges; a memory of M points, called the line memory, for successively receiving the signal charges stored by each line; a device for removing the parasitic charges associated with the line memory; and a CCD-type (charge coupled device) shift register receiving in parallel the content of the line memory and supplying in series the image scanning electric signal.